Increasing the injectivity index and productivity index of wells

ABSTRACT

The injectivity index of injection wells and the productivity index of producing wells in fluid communication with a hydrocarbon-bearing formation is improved by injecting about 1500 gallons of a micellar dispersion per vertical foot of hydrocarbon-bearing formation, thereafter injecting about 1-500 gallons of a mobility buffer per vertical foot of hydrocarbonbearing formation, and injecting sufficient displacing fluid to displace the micellar dispersion to a radius of at least about 7.5 feet from the well bore, and thereafter injecting about 1-500 gallons of a solution capable of counteracting the decrease in permeability caused by the mobility reducing agent in the mobility buffer. For example, the micellar dispersion can be followed by a mobility buffer containing water and a partially hydrolyzed, high molecular weight polyacrylamide and this followed by 0.1-50 volumes of water per volume of mobility buffer and this, in turn, followed by about 1-500 gallons of a sodium hypochlorite solution per vertical foot of hydrocarbon-bearing formation. The displacing fluid and the mobility buffer can be substantially hydrocarbon in an &#39;&#39;&#39;&#39;oil-wet&#39;&#39;&#39;&#39; reservoir.

FIPTwlZi XR 3961489774 0 United States Patent [is] 3,648,774 Kirk 5]Mar. 14, 1972 [54] INCREASING THE INJECTIVITY INDEX PrimaryExaminer-Stephen J. Novosad AND PRODUCTIVITY INDEX OF Attorney-Joseph C.Herring, Richard C. Willson, Jr. and Jack WELLS L. Hummel [72] Inventor:Walter B. Kirk, Robinson, Ill. [57] ABSTRACT [73] Assignee: Marathon OilCompany, Findlay, Ohio ,The injectivity index of injection wells and theproductivity I 7 index of producing wells in fluid communication with a[22] 1970 hydrocarbon-bearing formation is improved by injecting 2 Appl21 2 about l-500 gallons of a micellar dispersion pervertical foot ofhydrocarbon-bearing formation, thereafter injecting about 1-500 gallonsof a mobility buffer per vertical foot of 166/305 R, 1 6/273hydrocarbon-bearing formation, and injecting sufiicient dis- [51] Int.Cl ..E2lb 43/22 placing fluid to displace the micellar dispersion to aradius of [58] Field of Search ..l66/305 R, 273, 274, 275, 252; at leastabout 7.5 feet from the well bore, and thereafter in- 252/855 D jectingabout 1-500 gallons of a solution capable of counteracting the decreasein permeability caused by the mobility [56] References Cit d reducingagent in the mobility buffer. For example, the mice]- lar dispersion canbe followed by a mobility bufi'er containing UNITED STATES PATENTS waterand a partially hydrolyzed, high molecular weight polyacrylamide andthis followed by 0.1-50 volumes of water 3,460,622 8/1969 Davis, Jr...166/273 X per volume of mobility buffer and this in mm, followed by3,497,006 2/l970 Jonesetal...

...,.l66/273 3,506,070 4/1970 Jones u about I 500 gallons of a SOdlUI'llhypochlonte solution per vertical foot of hydrocarbon-bearing formation.The displac- 3,537,523 I H1970 Gogarty el al... ..l66/305 R i g fluidand the mobility buffer can be Substantially hy 3,482,635 12/1969 Pasini..l66/305 R bon in an reservoin 3,554,289 l/l97l Webb ..l66/305 R 14Claims, No Drawings INCREASING TIIE INJECTIVITY INDEX AND PRODUCTIVITYINDEX OF WELLS BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to improving the injectivity index of injectionwells and to improving the productivity index of producing wells. Thisis accomplished by injecting a micellar solution followed by a mobilitybuffer and this, in turn, followed by a displacing fluid and lastlyfollowed by a solution to increase the relative permeability to the flowof water. The micellar dispersion is comprised of hydrocarbon,surfactant, and aqueous medium. The mobility buffer can be hydrocarbonor water and contains a mobility reducing agent. The displacing fluidcan be hydrocarbon or water.

2. Description of the Prior Art U.S. Pat. No. 2,356,205 to Blair et al.teaches that the 1 injection wells. Gogarty teaches that the mobility ofthe micellar dispersion can be about equal to or less than the mobilityof fluids in the reservoir ahead of the dispersion. Water is injectedafter the micellar dispersion to displace it out into the reservoir.

U.S. Pat. No. 3,467,194 to Kinney and Jones teaches the stimulation ofproducing wells using water-extemal micellar dispersions.

U.S. Pat. No. 3,470,958 to Kinney teaches stimulation of productionwells by injecting an oil-external micellar dispersion and this followedby hydrocarbon to displace the micellar dispersion out into thereservoir. The hydrocarbon is preferably crude oil characteristic of theformation.

U.S. Pat. No. 3,474,865 to Gogarty and Jones teaches stimulation ofinjection wells using water-extemal micellar dispersions.

Applicant has discovered a novel method of increasing the injectivityindex of injection wells as well as the productivity index of producingwells. This is an improvement over the stimulation technology taughtabove.

SUMMARY OF THE INVENTION The injectivity index and productivity indexare increased y a. injecting into the hydrocarbon-bearing formationabout 1-500 gallons of micellar dispersion per vertical foot of theformation, followed by b. injecting about 1-500 gallons of a mobilitybuffer per vertical foot of the formation, and this followed by c.injecting a displacing fluid to substantially displace the micellardispersion to a radius of at least about 7.5 feet from the well bore,and thereafter d. injecting a fluid to increase the reduced permeabilitycaused by the mobility buffer. The mobility buffer can be an aqueoussolution containing a partially hydrolyzed, high molecular weightpolyacrylamide. The displacing fluid can be water and the fluidfollowing the displacement fluid can be an aqueous solution containingabout 01-30% of sodium hypochloritethe sodium hypochlorite increases therelative penneability of the formation that was adversely affected bythe polyacrylamide.

DESCRIPTION OF PREFERRED EMBODIMENTS OF INVENTION The micellardispersion useful with this invention includes both oil-external andwater-extemal. The micellar dispersion I is comprised of hydrocarbon,aqueous medium, surfactant and of hydrocarbon, about 10% to about 95%water, at least about 4% surfactant, about 0.01% to about 20% or more ofcosurfactant, and about 0.001% to about 5% by weight of electrolyte.Examples of useful micellar dispersions include those defined in U.S.Pat. Nos. 3,254,714 and 3,275,075 to Gogarty et al.; U.S. Pat. No.3,307,628 to Sena; U.S. Pat. No. 3,330,343 to Tosch et al.; U.S. Pat.No. 3,497,006 to Jones et al., and Ser. Nos. 693,099 and 693,125, filedDec. 26, 1967 by Jones. The hydrocarbon, aqueous medium, surfactant,cosurfactant (also identified as semipolar organic compound andcosolubilizer) and electrolyte useful with this invention include thesecomponents identified within the above-identified patents and patentapplications.

In general, the surfactant can be cationic, nonionic, and anionic. Thehydrocarbon can be crude oil, partially refined fractions of crude oil,refined fractions of crude oil, synthesized hydrocarbon, unreactedhydrocarbon within the surfactant, etc. The aqueous medium can be softwater, brackish water or a brine water. If the water contains ions, itis preferred that the ions are compatible with the subterraneanformation, including fluids and reservoir rock. The cosurfactant can bean alcohol, ester, aldehyde, amine, amino compound ketone, ether, orcombination of these functional groups within the same molecule or alike material-containing about one to about 20 carbon atoms. Alcoholsare preferred examples include isopropanol, amyl alcohols, 1- and2-hexanol, and alcohols such as 2-butoxyethanol. The electrolyte can bean inorganic or organic electrolyte and is preferably one that iscompatible with the ions within the subterranean formation.

The mobility buffer can be substantially aqueous or substantiallyhydrocarbon. It contains a mobility reducing agent which effectivelyreduces the permeability to the flow of fluids, e.g., water orhydrocarbon. The purpose of the mobility buffer is to buffer or protectthe micellar dispersion from invasion by a subsequent drive fluid. Bythis manner, better mobility control can be effected in the immediatevicinity of the well bore and a more efficient and uniform displacementof the micellar dispersion out to a radius of at least about 7.5 feetcan be effected. Examples of useful mobility reducing agents includepolysaccharides, glycerides, high molecular weightalcohols, highmolecular weight organic molecules having hydrophilic groups attached tothe molecule and optionally containing other groups on the molecule. Aparticularlyuseful mobility reducing agent is a partiallyhydrolyzed highmolecular weight polyacrylamide, e.g., the Pusher products marketed byDow Chemical Company. However, any chemical is useful with the mobilitybuffer as long as it is compatible with hydrocarbon and/or water andeffectively reduces the mobility of the mobility buffer flowing withinthe subterranean formation.

The mobility buffer is followed by a displacing fluid which can besubstantially hydrocarbon or substantially aqueous. Where thesubterranean formation is an oil-wet" system, it is preferred that themobility buffer be substantially hydrocarbon and that the displacingfluid be substantially hydrocarbon. However, where the reservoir is awater-wet" system or the well is an injection well, it is preferred thatthe mobility bufl'er be substantially aqueous and that the displacingfluid be an aqueous drive fluid. Examples of useful aqueous drive fluidsinclude water containing ions characteristic of the subterraneanformation or the aqueous medium can be a soft water, a brine water, or abrackish water.

The displacing fluid is followed by a fluid to increase the relativepermeability to the flow of fluids characteristic of the subterraneanformation. The permeability of the subterranean formation is generallyadversely affected by the mobility reducing agents. For example, apartially hydrolyzed, high molecular weight polyacrylamide tends todecrease the relative permeability to the flow of water. However, anaqueous diminished permeability caused by the polyacrylamide is overcomeby injecting the sodium hypochlorite solution. Examples of usefulconcentrations include about 0.1% to about 30% of the sodiumhypochlorite in the aqueous medium. More preferably from about 1% toabout 3% is useful. Other examples of useful agents to increase therelative permeability to the flow of fluids include any oxidizing agentthat is compatible with the formation and the particular medium theagent is dissolved in. For example, sodium hydroxide, potassiumhydroxide, and like materials are useful with the invention.

Regarding the volume amounts useful with the invention, about 1 to about500 gallons and preferably about 5 to about 250 gallons and morepreferably about 25 to about 200 gallons of micellar dispersion pervertical foot of hydrocarbonbearing formation are useful.

The mobility buffer can be injected in amounts of about 1 to about 500gallons, preferably 5 to about 250 gallons of the mobility buffer pervertical foot of formation. The preferred mobility buffer is an aqueoussolution containing partially hydrolyzed, high molecular weightpolyacrylamidesthis is preferred where the formation is a water-wetsystem or the well is an injection well. Preferably, the mobility bufferhas a mobility that is greater than the micellar dispersion injectedinto the formation, it can be greater than the mobility of formationfluids flowing in the formation. Also, it can be about equal to or aboutless than the mobility of the back portion of the micellar dispersion.More preferably, the mobility of the mobility buffer is equal to thesquare root of the mobility of the micellar dispersion times themobility of the displacing fluid that displaces the mobility buffer.

The displacing fluid can be in volumes of about 1 to about 500 or moregallons per vertical foot of the hydrocarbon-bearing formation.Preferably, sufficient amounts of displacing fluid are injected todisplace the micellar dispersion out to a distance of at least about 7.5feet and more preferably about 12-15 feet in radius from the well bore.Most preferably, sufficient displacing fluid is injected to displace themobility buffer to a radius of at least about 7.5 feet and morepreferably to a radius of about 15 feet from the well bore.

About 1-500 gallons and more preferably about -200 gallons of the fluidcontaining the agent to increase the relative permeability to the flowof fluids is injected per vertical foot of hydrocarbon-bearingformation. It is preferred that sufiicient fluid be injected to contactsubstantially all of the reservoir in a radius of at least about 7.5feet and more preferably about feet from the well bore. This is desiredso that the oxidizing agent can effectively contact and overcome theadverse permeability caused by the mobility reducing agent. For example,about equal amounts of this fluid can be injected based on the volume ofthe mobility bufi'er fluid.

It is not intended that this invention be limited by the specificstaught herein. Rather, all equivalents obvious to those skilled in theart are intended to be incorporated within the scope of the invention astaught within the specification and appended claims.

What is claimed is:

l. A process of increasing the injectivity index of injection wells andthe productivity index of producing wells in fluid communication with ahydrocarbon-bearing formation, the process comprising injecting into thehydrocarbon bearing formation in fluid communication with the particularwell:

1. about 1500 gallons of a micellar dispersion per vertical foot of thehydrocarbon-bearing formation, thereafter,

2. injecting a mobility buffer slug, and then,

3. injecting sufficient displacing fluid to substantially displace themobility buffer to a distance of at least about 7.5 feet in radius fromthe well bore, and then,

4. injecting sufficient amounts of a fluid different from the displacingfluid of step 3 and which will act on the formation to substantiallyincrease the relative permeability to the flow of fluids through thereservoir wherein a decreased permeability was caused by a mobilityreducin agent within the mobility buffer. 2. e process of claim Iwherein the micellar dispersion 1S comprised of hydrocarbon, surfactant,and aqueous medium.

3. The process of claim 2 wherein the micellar dispersion optionallycontains cosurfactant and/or electrolyte.

4. The process of claim 1 wherein the mobility buffer is an aqueoussolution comprised of a partially hydrolyzed, high molecular weightpolyacrylamide.

5. The process of claim 1 wherein from about 1 to about 500 gallons of amobility buffer per vertical foot of hydrocarbon-bearing formation isinjected into the formation.

6. The process of claim 1 wherein from about 0.1 to about 50 volumes ofwater per volume of the mobility buffer is injected into the reservoir.

7. The process of claim 1 wherein said fluid of step 4 comprises about 5to about 250 gallons of a sodium hypochlorite solution per vertical footof hydrocarbon-bearing reservoir.

8. A process of increasing the injectivity index of an injection well influid communication with a hydrocarbon-bearing formation, the processcomprising:

1. injecting into the formation about 1 to about 500 gallons of amicellar dispersion per vertical foot of the formation,

2. injecting into the formation about 1-500 gallons of a mobility bufferper vertical foot of the formation,

3. injecting sufficient water into the formation to substantiallydisplace the micellar dispersion to a radius of at least about 7.5 feetfrom the well bore,

4. injecting about 1 to about 500 gallons of an aqueous solutioncontaining sodium hypochlorite, and,

5. thereafter continuing the injection of water into the injection well.

9. The process of claim 8 wherein from about 5 to about 250 gallons ofthe mobility buffer per vertical foot of the formation is injected.

10. The process of claim 8 wherein the mobility buffer contains amobility reducing agent which is a partially hydrolyzed, high molecularweight polyacrylamide.

11. The process of claim 8 wherein sufficient water is injected tosubstantially displace the mobility buffer to a distance of at leastabout 7.5 feet in radius from the well bore.

12. The process of claim 8 wherein from about 0.5 to about 30 volumes ofwater per volume of mobility buffer is injected into the reservoir.

13. The process of claim 8 wherein from about 10 to about 200 gallons ofthe sodium hypochlorite solution per vertical foot ofhydrocarbon-bearing formation is injected into the formation.

14. The process of claim 8 wherein the sodium hypochlorite solutioncontains from about 0.1 to about 30 percent of sodium hypochlorite.

2. injecting into the formation about 1-500 gallons of a mobility bufferper vertical foot of the formation,
 2. The process of claim 1 whereinthe micellar dispersion is comprised of hydrocarbon, surfactant, andaqueous medium.
 2. injecting a mobility buffer slug, and then, 3.injecting sufficient displacing fluid to substantially displace themobility buffer to a distance of at least about 7.5 feet in radius fromthe well bore, and then,
 3. The process of claim 2 wherein the micellardispersion optionally contains cosurfactant and/or electrolyte. 3.injecting sufficient water into the formation to substantially displacethe micellar dispersion to a radius of at least about 7.5 feet from thewell bOre,
 4. injecting about 1 to about 500 gallons of an aqueoussolution containing sodium hypochlorite, and,
 4. The process of claim 1wherein the mobility buffer is an aqueous solution comprised of apartially hydrolyzed, high molecular weight polyacrylamide.
 4. injectingsufficient amounts of a fluid different from the displacing fluid ofstep 3 and which will act on the formation to substantially increase therelative permeability to the flow of fluids through the reservoirwherein a decreased permeability was caused by a mobility reducing agentwithin the mobility buffer.
 5. The process of claim 1 wherein from about1 to about 500 gallons of a mobility buffer per vertical foot ofhydrocarbon-bearing formation is injected into the formation. 5.thereafter continuing the injection of water into the injection well. 6.The process of claim 1 wherein from about 0.1 to about 50 volumes ofwater per volume of the mobility buffer is injected into the reservoir.7. The process of claim 1 wherein said fluid of step 4 comprises about 5to about 250 gallons of a sodium hypochlorite solution per vertical footof hydrocarbon-bearing reservoir.
 8. A process of increasing theinjectivity index of an injection well in fluid communication with ahydrocarbon-bearing formation, the process comprising:
 9. The process ofclaim 8 wherein from about 5 to about 250 gallons of the mobility bufferper vertical foot of the formation is injected.
 10. The process of claim8 wherein the mobility buffer contains a mobility reducing agent whichis a partially hydrolyzed, high molecular weight polyacrylamide.
 11. Theprocess of claim 8 wherein sufficient water is injected to substantiallydisplace the mobility buffer to a distance of at least about 7.5 feet inradius from the well bore.
 12. The process of claim 8 wherein from about0.5 to about 30 volumes of water per volume of mobility buffer isinjected into the reservoir.
 13. The process of claim 8 wherein fromabout 10 to about 200 gallons of the sodium hypochlorite solution pervertical foot of hydrocarbon-bearing formation is injected into theformation.
 14. The process of claim 8 wherein the sodium hypochloritesolution contains from about 0.1 to about 30 percent of sodiumhypochlorite.